Yade

handling post-breakage rolling in a cohesive contact

Asked by behzad

Hi there,

I have a cohesive contact which can break if shearAdhesion or normalAdhesion values are met by the contact force.

These lines handle the normalAdesion part:

  if (geom.penetrationDepth <0 && phys.fragile && phys.normalAdhesion > 0 && phys.normalForce.norm() > phys.normalAdhesion) {
     phys.cohesionBroken= true;
  return false;
        }

However, the problem is in shearAdhesion part. What's the correct way to state the breakage of a cohesive contact by shear force and include the friction effect as well?
 i.e. if the shearForce.norm() > shearAdhesion, break the cohesion and now as the friction angle is bigger, the movement is more difficult.

I got this from the other contact models in Yade. But, effect of frictionAngle is not correct this way. Because, bigger friction angle doesn't make the particles reluctant to move.

   if (phys.fragile && phys.shearAdhesion > 0.0 && phys.shearForce.norm() > phys.shearAdhesion) {
     phys.SetBreakingState();

  const Real maxFs = phys.normalForce.squaredNorm() * std::pow(phys.tanFrictionAngle,2);
  Real ratio = maxFs/ phys.shearForce.norm();
  phys.shearForce *= ratio;
        }

Can someone help me out?
Thanks

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Bruno Chareyre (bruno-chareyre) said : 		#1

Hi,

> if the shearForce.norm() > shearAdhesion, break the cohesion and now as the friction angle is bigger, the movement is more difficult.

If you don't understand why friction angle should be bigger.
Also, what is the relation to rolling. It is not very clear to me ,sorry.

Bruno

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Bruno Chareyre (bruno-chareyre) said : 		#2

"If you don't understand" -> "I don't understand"
A weird auto-completion got me there.

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behzad (behzad-majidi) said : 		#3

Hi,

this is the question: how we include friction coefficient(frictionAngle) in post-breakage equations?

- If you don't understand (I don't understand) why friction angle should be bigger.

I mean, if the contact adhesion is broken and two spheres are free to move/roll, as the friction coefficient (here frictionAngle) is bigger the movement/rolling of the spheres must be more difficult.

cheers,
Behzad

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